Documents can either be created by individuals or by a group of individuals. Different documents created can be related or have overlapping content in that they relate to common objects and phenomena. In such circumstances, required relationships between data in one document and data in the same or other documents may be formalised as a set of consistency rules defining those relationships.
An example of a simple consistency rule might be that data in one document which also appears in another document is considered to relate to the same object or phenomena. More complex formal relationships can exist within documents such as design specification documents which are intended to contain data which is represented in different documents in different ways in a pre-defined manner.
In circumstance where new documents, document types and consistency rules may be added at any time it becomes difficult to ensure that, during the production of a set of documents, the set of documents fulfils all of the requirements of a formal set of consistency rules at relevant key points within the production process. This is particularly the case since during the production of a set of documents, it is inevitable that on occasions some consistency rules will not be satisfied. Thus for example where it is required that data present in one document also appears in another, when data is initially entered for the first document the other document may not immediately reflect the change made to the first document.
Where documents are generated in distributed organisations by large numbers of individuals it becomes impractical to limit the production of documents to ways which ensure as far as is possible that the consistency of a set of documents is constantly maintained. Also, with large sets of documents it becomes very difficult for formal consistency relationships to be checked manually as searching through the data of a large set of documents is time consuming and errors occur.
The present invention aims to provide a means by which data which is intended to comply with formal consistency relationships defined by a set of consistency rules can be monitored whilst tolerating the entry of data which does not fulfil the required relationships.
In accordance with one aspect of the present invention there is provided a computer apparatus comprising:                means for generating a first set of structured documents containing data;        means for defining a set of consistency rules defining relationships which are intended to be fulfilled by the data within the first set of documents; and        means for generating a second set of documents containing data of said first set of documents, wherein the data of the second set of documents is linked on the basis of whether said data does or does not fulfil the relationships defined by said consistency rules.        
By providing means by which a linked set of documents can be generated, users are then able to view data which either fulfils or does not fulfil a consistency rule in the context of the document where that data appears.